Optical system for guiding a projectile



Aug. 27, 1968 v (3|RAULT 3,398,918

OPTICAL SYSTEM FOR GUIDING A PROJECTILE Filed Decf 5, 1966 4 Sheets-Sheet l LAUNCHING DEVICE Aug. 27, 1968 P. GIRAULT OPTICAL SYSTEM FOR GUIDING A PROJECTILE 4 4 Sheets-Sheet 2 Filed Dec.

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OPTICAL SYSTEM FOR GUIDING A PROJECTILE Filed Dec. 5, 1966 4 Sheets-Sheet 5 United States Patent OPTICAL SYSTEM FOR GUIDING A PROJECTILE Pierre Girault, Paris, France, assignor to SFCompagnie Generale de Telegraphie Sans .Fil, a corporation of France Filed Dec. 5, 1966, Ser. No. 599,139 Claims priority, application France, Dec. 6, 1965,

11 Claims. (or. 244-313 ABSTRACT OF THE DISCLOSURE There is a problem in guiding a projectile towards a target over a range of several kilometers, where the dimensions and weight .of the projectile are limited. Teleguiding systems implying the use of a wire cannot be used because of the distance to be covered and because of the speed limitation they involve. Also radio guidance systems using Hertzian waves are not satisfactory since, considering in particular the distances to be covered, they can hardly comply with the limitations which are generally imposed in so far as weight, volume and costs are concerned. In addition, they are jamming sensitive.

In order to guide a light anti-tank missile towards its target, it has been attempted to. use a sighting glass for acquiring the target and, associated therewith, a very powerful light transmitter for guiding the said missile along a trajectory which deviates only little from the line of sight. Such beams of light can be produced at present with all the characteristics which are desirable by means of lasers.

According to the present invention there is provided an optical beam-rider guidance system for guiding a missile from a launching base to a target, wherein said launching base comprises: sighting means having an optical axis for sighting said target; laser means generating a plurality of fan-shaped light beams crossing each other, means for deflecting said beams laterally of said axis and means for modulating said beams.

There is also provided a missile for a system as above mentioned, said missile comprising means for sensing the modulated energy carried by said beams, rudder means for controlling the trajectory of said missile and guidance means coupling said rudder means to said sensing means.

For a better understanding of the invention and to show how the same may be carried into effect, references will be made to the accompanying drawings, in which:

FIG. 1 shows a first embodiment of the guiding system according to the invention;

FIG. 2 is a block diagram of the system of FIG. 1;

FIG. 3 is a second embodiment of the guiding system according to the invention; and

FIG. 4 is a block diagram of the system of FIG. 3.

FIG. 1 shows an optional maser or laser 1 continuously or intermittently transmitting an only slightly divergent beam of light aligned parallel with the axis oz. The radiated energy is preferably within the infrared band so that it is not visible. It may be produced by a ruby or a gas laser, according to whether a pulsed or continuous emission is required. The beam coming from the source 1 passes through an optical modulator comprising a pair of Efihdflld Patented Aug. 27, 1958 crossed polarizers 2 and 3 between which is located an electrically birefringent medium 4 Under the action of a modulating voltage U applied by means of electrodes to the birefringent medium, the beam is intensity modulated without its very small divergence being thereby affected. This amplitude modulated beam passes then through an optical anamorphotic device, consisting of a fixed cylindrical lens 5 and a mobile cylindrical lens 6,. These two lenses cooperate in substantially increasing the divergence of the beam in the plane of curvature of the lenses, without altering it in the plane normal thereto. One obtains finally a fan shaped modulated beam of light with a divergence less than 1 milliradian in the plane containing the axis oz. The divergence a in the plane normal to the former is controlled by modifying, by means of a servo-motor 8 the distance between the lenses 5 and 6 The incidence of the axis oz relative to the spread or fan shaped beam thus obtained is controlled by pivoting the optical assembly 5 6,, by means of a servomotor 9,,. The projectile 16 is represented near the line of sight oz which coincides with the axis of the launching device 13. According to the invention, the projectile pro ceeds inside a corridor, centred on the line of sight, and whose walls are formed by the beams 7 and by similar beams 7 7 and 7,, which intersect one another. A programmer 11, which is started at the moment the missile is launched, works out the orders which actuate the servomotors 8,, and 9,, corresponding to each beam so that the beams form continuously around the projectile 10 during its progression towards the target, a closed outline of predetermined dimensions, for example, not exceeding those of the target. The projectile 10 is self-guided in such a way that it remains inside the closed outline defined by the beams 7 7, 7, and 7 This is a sort of beam-riding guidance.

FIG. 2 shows the block diagram of the system of FIG. 1. It consists of two parts, one located at the luanching base and the other inside the missile 10.

The launching base comprises the laser 1 equipped with its supply source 12; the light beam produced thereby passes, after optical division, which may be achieved, for example, as shown in FIG. 3, through the optical modulators 4,, 4 4 and 4 which are respectively controlled by the modulating voltages U U U and U from the oscillators 14 14 14 and 14 The beams pass then through anamorphosers 6,, 6 6 and 6, which spread them out and make them converge under the control of a programmer 11 which depends on the launching system 13.

The missile comprises a detecting system consisting of a collector lens 15, a filter 16, centered on the optical frequency transmitted by the laser 1, and a photo-electric element 17. The photo-electric element 17 is connected to a receiver 18, having four outputs a, b, c and d at which appear separately the detection signals originating from the beams 7 7 7 and 7,

These signals are applied as control signals to a known system 19 comprising a gyroscope and a computer which works out orders M and N for the correction of the trajectory. These orders actuate the rudders 23 and 24 by means of servo-motors 21 and 22.

As soon as the missile has been launched, the launching base projects into space the four beams 7 7 7 and 7, which differ from one another by their respective modulation frequencies f,,, f f and f These beams are spread out and orientated according to the programme produced by the programmer 11 and surround completely the missile as a closed contour, centered on the line of sight. When the missile tends to deviate from this sight line, indicated by the axis oz in FIG. 1, it encroaches, for example, on the beam 7,, which acts then on the photoelectric element 17 and causes the appearance of an 3 output voltage at the output a of the receiver 18. This voltage acts on the computer 19, associated to the gyroscope 20, and supplies piloting orders M and N, which actuate the rudders 23 and 24. As a consequence, the flight direction is corrected and the projectile moves away from the beam 7 while remaining inside the corridor.

With this system it is therefore sufficient to sight a target and to create around the line of sight a corridor formed by the beams 7 7 7 and 7 for guiding the projectile, by means of successive ricochets or bounces within the interior of this corridor, until it reaches the target at the end of its progression. This is, therefore, a selfguiding system by all-or-nothing and everything happens as if the projectile were guided within a rigid tube from the walls of which it bounces successively without being able to break through them.

It follows from the foregoing that the projectile is guided in a by all-or-nothing manner, since the change in the trajectory is effected by interception of one or two of the beams of light forming the lateral walls of a corridor. Naturally, this corridor could be partitioned into a plurality of further corridors by means of intermediate beams, in order to achieve a more gradual modification of the trajectory.

As an extreme, one could even image an infinity of beams which would define in space a guiding volume making possible a proportional control. However, the production of a large number of beams would complicate the optical system at the launching base. Therefore the invention provides a proportional guidance system by means of two beams sweeping the guiding volume in directions perpendicular to each other.

FIG. 3 shows a laser 1 emitting a beam with only slight divergence, which beam is divided into two by means of a reflecting device 25. The two reflected beams propagate respectively through polarizers 2 and 2 the birefringent media 4,, and 4 and the polarizers 3,, and 3 which cooperate so as to modulate the light intensity of the beams by means of modulating voltages U and U The modulated beams are then reflected by vibrating mirrors 26,,, 26 actuated, respectively, by servo-motors 27 and 27 The beams reflected by the vibrating mirrors are rendered anamorphous by means of optical devices comprising, respectively, the fixed cylindrical lenses 5 and 5 and the movable cylindrical lenses 6,, and 6 Two beams 7 and 7 at right angles to each other and very flat, are then obtained as shown in FIG. 3. The beam 7 performs a sweeping along the axis 0 and the beam 7 sweeps along the axis 0x.

FIG. 4 shows a block diagram of the guiding system of FIG. 3. The beam emitted by the light source 1 is divided optically, by means of an optical device 25 into two beams, which pass, respectively, through the optical modulators 4,, and 4 These beams are respectively amplitude modulated by means of the voltage generators 29 and 29,, which are in turn frequency modulated within distinct frequency hands by a sweep generator 28. Bandpass filters 31 and 31 are provided on board the projectile for separating the signals in accordance with the modulation they undergo. From the modulators 4,, and 4 the modulated beams pass through optical anamorphous devices 6,, and 6 and pass through the deviators 27 27 respectively whereby the beams perform a sweep in synchronism with the sweep signal produced by the generator 28. The sweep of the beams and the amplitude of the sweep are also controlled by a programmer 11 controlled by the launching device 13.

On board the projectile is a collector lens 15, a filter 16 centered on the emission optical frequency of the source 1 and a photo-electric element 17 which feeds an amplifier 30.

The output of the amplifier 30 is connected to separating filters 31 and 31 mentioned above, which respectively feed the frequency discriminators 32 and 32 The position information supplied by the discriminators 32 and 32 is applied simultaneously to two computers 19 and 19,, which, by means of angular information, supplied by the gyroscope 20, work out the orders M and N for guiding the projectile. The orders M and N are applied to servo-motors 21 and 22 which actuate the rudders 23 and 24.

When the projectile is launched towards the target, the source 1 transmits a beam of light, divided into two parts which pass, respectively, through the modulators 4 and 4 to which are respectively applied two modulating voltages which are frequency modulated with different frequency bands voltages. The modulation frequencies are connected with the voltage supplied by the generator 28, since the same controls the oscillators 29 and 29 This voltage is also applied to the deviators 27 and 27 which cause the beams issuing from the modulators 4 and 4 to perform a sweeping along the planes yoz and xoz respectively. These angular sweeps are synchronized with the frequency excursion of the generators 29 and 29 so that each orientation of a beam corresponds to a certain value of the optical modulation frequency. The beams available at the output of the deviators 27 and 27, are rendered anamorphous by the anamorphotic devices 6 and 6 which emit the flattened beams 7 and 7,, into space. From the launching, a programmer 11 controls the anamorphotic devices 6,, and 6 and the deviators 27 and 27 so as to adjust the spreading out of the beams and the amplitude of the sweep as a function of the distance through which the projectile 10 has travelled. This control is assured from the moment of launching which is determined by the launcher 13.

The projectile flying inside the pyramid shaped volume centred on the line of sight is swept by the two beams 7 and 7 Its detection system receives each time the missile is swept by the beams 7 and 7 a pair of luminous information signals which have instantaneous frequencies which determine the position of the projectile transversally relative to the line of sight oz. The information items are translated by the photo-electric cell 17 and the amplifier 30 into electrical signals which are decoupled by means of filters 31 and 31 The AC. voltages at the outputs of the filters are then applied to the discriminators 32 and 32;, which supply, respectively, the trajectory deviations E and E as shown in FIG. 3. These deviations are then converted by the computers 19,, and 19 into piloting orders M and N, taking into consideration the angular information given by the gyroscope 20. These orders act on the rudders 23 and 24 through servo-motors 21 and 22. In this way deviations from the trajectory are proportionally corrected which assures the accurate guiding of the projectile towards the target.

By way of example, a sweep frequency of the beams of the order of 20 c./s. and an amplitude of 2.5 in. measured at a distance of 200 m. from the launching base may be provided. The minimum aperture of the light beams is of the order of milliradians. Frequency modulation bands used are centred at about 20 and 30 kc./s., respectively, with a frequency excursion of 10 percent. Under these conditions the power of the laser source must be 3 milliwatt to obtain a signal-to-noise ratio of more than 12 db.

According to the invention, on board the projectile an optical filter 16 is used, which is centred on the transmission frequency of the source 1. This filter makes it possible to eliminate in a substantial manner disturbances caused by ambient light.

As inertial guiding system a gyroscope may be used. The inertia axis of the gyroscope supplies the angular information for taking into account the rotation of the projectile about itself. The computers which issue the piloting orders comprise, by way of example, sine-cosine potentiometers supplied by the detection signals in the case of a frequency modulation following a sinusoidal law.

Of course, the invention is not limited to the embodiments described and shown.

For example, without departing from the scope of the invention, the beams can be differentiated from each other by means of a modulation other than the frequency modulation. For example, the light energy may be pulse modulated to form trains of pulses of variable width wherein this width is a function of the instantaneous position of the beam in the space.

What is claimed is:

1. An optical beam-rider guidance system for guiding a missile from a launching base to a target, wherein said launching base comprises: sighting means having an optical axis for sighting said target; laser means generating a plurality of fan-shaped light beams crossing each other, means for deflecting said beams laterally of said axis and means for modulating said beams.

2. A missile for a system as claimed in claim 1, said missile comprising means for sensing the modulated energy carried by said beams, rudder means for controlling the trajectory of said missile and guidance means coupling said rudder means to said sensing means.

3. A missile as claimed in claim 2, wherein said sensing means comprise photoelectric transducer means, means for focusing on said transducer means the light energy of said beams and, associated with said focusing means optical filtering means rejecting the radiations having a wavelength ditferent from the wavelength of said laser means.

4. A guidance system as claimed in claim 3, wherein said launching device further comprises means for actuating said deflecting means according to a predetermined program starting from the instant of the launching.

5. A guidance system as claimed in claim 4, wherein said generating means comprise at least one laser source radiating a beam of light having a small divergence and anamorphotic means for spreading said beam in a transverse direction to form a fan-shaped beam.

6. A guidance system as claimed in claim 5, wherein said modulation means comprise a pair of crossed polarizers and electro optical modulator means positioned between the latter.

7. A guidance system as claimed in claim 6, wherein said fan shaped beam generating means includes control means for causing said fan-shaped beams to build up substantially the lateral faces of a pyramid having a symmetry axis aligned on said optical axis, said pyramid having a base smaller than the area of said target.

8. A guidance system as claimed in claim 6 wherein said modulation means comprise a plurality of oscillators having distinct oscillation frequencies.

9. A missile for a system as claimed in claim 8 wherein said guidance means comprise a plurality of band pass filters coupled to said transducer means and respectively tuned to said frequencies, means for detecting said modulation signals at the respective outputs of said filters, computer means having first inputs coupled to said detecting means, second inputs and outputs; said second inputs being coupled to gyroscopic means and said outputs of said computer means being coupled to said rudder means.

10. A guidance system as claimed in claim 6, wherein said laser means generate a first and a second fan-shaped beam intersecting each other at right angles; said launching base further comprising a first and a second sweep generator; said deflecting means comprising first and second scanning devices respectively controlled by said first and second sweep generators for respectively sweeping said first and second beams through the volume of a pyramid having a symmetry axis aligned with said axis and a base smaller than said target; first and second frequency modulated oscillators for supplying said modulating signals, respectively controlled by said first and second sweep generators, said modulation signals lying in distinct bands of frequencies.

11. A missile for a system as claimed in claim 10 wherein said guidance means comprise: a first and a second band pass filter, having outputs and coupled to said transducer for separating the modulation signals respectively carried by said first and second beams; first and second discriminator means respectively coupled to the outputs of said first and second filters, computer means having two inputs respectively coupled to said discriminator means, further inputs and outputs; said further inputs being coupled to gyroscopic means and said outputs of said computer means being coupled to said rudder means.

References Cited UNITED STATES PATENTS BENJAMIN A. BORCHELT, Primary Examiner.

T. H. WEBB, Assistant Examiner. 

